pcf1252 NXP Semiconductors, pcf1252 Datasheet - Page 3

• Manufacturer Part Number: pcf1252
• Description: Threshold Detector And Reset Generato
• Manufacturer: NXP Semiconductors

Philips Semiconductors
PINNING
FUNCTIONAL DESCRIPTION (see Fig.1)
The PCF1252-X contains:
The PCF1252-X family is comprised of 10 versions with
different factory-programmed voltage trip-points (V
see Chapter “Characteristics”.
Supply
The supply voltage (V
compared, via comparator 1, with the internal reference
voltage.
POWF (see Fig.3)
The POWF output is:
Power-on reset (SELECT = LOW)
As V
at RESET. The duration of the reset pulse (t
determined by the value of the external capacitor (C
maximum 1 F, see Fig.8) connected to CT. With no
external capacitor connected, C
value of 100 pF. If SELECT is HIGH, the reset pulse is
inverted.
Power failure
During a power-off condition (V
LOW. After a time delay (t
RESET goes HIGH. Any POWF assertion (V
will result in a subsequent RESET pulse.
1998 Apr 16
CT
SELECT
COMIN
V
COMOUT
RESET
POWF
V
SYMBOL
SS
DD
A precise factory-programmed voltage reference
Two comparators
A delay circuit.
LOW, if V
HIGH, if V
Threshold detector and reset generator
DD
rises past V
DD
DD
PIN
1
2
3
4
5
6
7
8
is below V
is above V
TRIP
connection for the external capacitor
select polarity or external reset input
comparator input
ground (0 V)
comparator output
reset output
power failure signal output
supply voltage
DD
, a positive reset pulse is generated
) is internally divided before being
TRIP
TRIP
S
), also determined by C
.
DESCRIPTION
DD
CT
< V
assumes a minimum
TRIP
), POWF goes
R
DD
) is
< V
TRIP
CT
TRIP
CT
,
;
),
)
3
Voltage trip-point
By selecting the voltage trip-point slightly higher than the
minimum operating voltage of the
microcontroller/microprocessor, there is sufficient time for
data storage before the power actually fails.
In order to prevent oscillations around the voltage
trip-point, a small hysteresis has been included, resulting
in a power-on switching point that is higher than the
voltage trip-point (minimum of 15 mV). The voltage
trip-point refers to the value at which power-off is signalled.
COMIN
Input to the second comparator (comparator 2).
When used in conjunction with an external voltage divider,
this allows a second point in the system to be monitored.
This input has no built-in hysteresis. When not in use
connect to V
depending on the voltage at COMIN:
handbook, halfpage
COMOUT = HIGH, if voltage at COMIN is above the
switch point V
COMOUT = LOW, if voltage at COMIN is below the
switch point V
SELECT
DD
COMIN
. COMOUT will be LOW or HIGH
V SS
SP
SP
CT
Fig.2 Pinning diagram.
(typically 1.30 V).
(typically 1.30 V).
1
2
3
4
PCF1252-X
PCF1252-X family
MGC916
7
6
5
8
Product specification
V DD
POWF
RESET
COMOUT